An elated Olunga took to his Instagram page to break the news, saying; New Roads, New Rivers, New Chapter. Beginning of another unfolded history.
Olunga joins Kashiwa after a season long spell at Spanish side Girona where he went on to make history by becoming the first Kenyan to score in La Liga as well as the first a Hat-trick in the Spanish league.
Popularly known as the 'Engineer', the former Gor Mahia forward spent an year at Ghuizhou Zhicheng joining in a record Sh450 million deal from Sweden top flight side IF Djurgardens in 2016.
He fell down the pecking order and joined Girona in search of more playing time.
The 24-year-old's transfer fee from Guizhou Zhicheng is believed to have cost Kashiwa Reysol $150,000 or ksh 15 million.
Olunga joins an array of other big football names in the fast rising J-league and he is set to face the likes of; Lukas Podolski, Andreas Iniesta and Fernando Torres.
His new side is currently 13th on the 18-team J1 League with 23 points from 20 matches. They next face 12th-placed Vegalta Sendai on Saturday 11th August at their Sankyo Frontier Stadium in the city of Kashiwa.
Olunga has previously featured for Kenyan premier league sides; Thika United, Tusker FC and Gor Mahia.